The present invention relates to the determination of the leanness of meat and more particularly to the determination of the leanness of meat from the relative abundance of gamma rays naturally emitted by the potassium-40 naturally found in lean meat.
It is well known that lean meat contains potassium. Potassium is found in protein but not in fat, and the determination of relative potassium content is indicative of the relative leanness and relative protein content of meat. A determination of relative potassium content therefore provides a method of grading meat.
One way of determining relative potassium content is to determine the relative number of gamma rays emitted by potassium-40, a naturally radioactive isotope of potassium constituting a known portion of naturally occurring potassium. Such gamma rays have a characteristic energy of 1.46 Mev. It is well known to utilize scintillation counters with differential pulse height analyzers to provide a measure of relative potassium-40 content and hence leanness of meat. See, for example, Pringle, Derek H., et al., "K.sup.40 Gammas Give Estimate of Lean Meat Content," Nucleonics, February 1961, pp. 74-78. In the Pringle et al., device, samples of meat were inserted in the well of a scintillation counter arrangement heavily shielded with lead. Only small samples could be inserted in the scintillation counter well which acted as a 4 pi measuring device.
Another 4 pi measuring device for measuring potassium-40 gamma rays, used for measuring leanness of beef on the hoof, is that shown in Keck, Charles R., et al., U.S. Pat. No. 3,376,417, which disclosed a massive array of heavily shielded scintillation counters in which array an entire animal was confined.
The cost of these massive 4 pi measuring devices heavily shielded on the outside has severely limited their use. According to the present invention no external shielding is required, and a simple probe is inserted into approximately the center of a bin of meat. The meat itself acts to shield the detector from ambient radiation, such as cosmic rays.
In the use of scintillation counters in well logging the earth shielded the detector from the effect of cosmic rays. However, this was not used in measurement of finite samples. See, for example, Youmans, A. H., U.S. Pat. No. 2,949,534. Probes have been used for placing scintillation crystals near the material being measured, as shown in Caha, A., et al., U.S. Pat. No. 2,931,905. However, this was simply to place the detector near the object to be measured, not to place the detector in the center of an object to be measured while utilizing the object being measured as a shield.